Good question Wayne! One of the secrets to optimal RIP calibration is to determine the optimal ink limits by looking for the chroma (saturation) peak, not maximum density, as many assume. As we increase inkload on pigment printers, density and chroma climb together. But at one point the chroma peaks and then starts to decline as density continues to climb. For pigment printers, we get the best results if we set the ink limiting right at the beginning of this peak. Then perform per channel linearization, then combined linearization, then determining the combined total ink limit and, finally, profile. High quality papers will easily hold this ink and allow for a very high total ink limit. Of course lesser quality budget papers will have a problem with this much ink and you'll be forced to back off from these peaks by an overall percentage (often just ~5%) and that's life with cheapo papers. Solvent printers will have problems with this much ink so I back off by 10% as a rule of thumb for the sake of keeping the TIL high. For photographic imagery we must prioritize keeping the TIL high even if it means backing off on the per channel limiting a little. Anyway...
The challenge here is using software that allows us to visually graph out these things as we play with ink load. For years I've encouraged various developers to come up with a simple application that would do this for us. I know I'd pay for that but I'm sure I'm a small minority. :-] I wish Curves2 would do this. If one is really familiar with the Mac version of ColorBurst RIP it can be used for this purpose. I use CB to analyze these things when I'm calibrating any other RIP. I don't want to take the time to write an entire article on this but you get the point, and something tells me Wayne, that you already know how to do this.